The Peach-Potato aphid Myzus persicae has traditionally been considered as the most important aphid vector of potato viruses. However in Scotland, Peach-Potato aphids generally fly later and in far lower numbers than in warmer countries and their relative scarcity generally makes this species less of a concern to potato growers. In some years, usually following a particularly mild winter, Peach-Potato aphids can present a very high risk of virus transmission, particularly Leaf Roll, within the Scottish seed potato crop.
Prolonged exposure to low winter temperatures are known to have lethal and sub-lethal effects on populations of M. persicae which, in Scotland, overwinter as larvae or apterous adults. Poor over-winter survival delays the build up of populations of this species in the forthcoming growing season. Prior to 2011, SASA had used the mean temperatures for January and February to predict when M. persicae will become active in the summer. In 2011, following an extremely cold December 2010, SASA predicted aphid activity based on the mean temperatures during the three-month period of December-February. We intend to continue to use the model based on the 3 month period.
During winter 2018-19, the mean temperatures were well above the mean over the last 50 years: 5.1°C at SASA (Edinburgh; mean = 4.0°C) and 4.1°C at JHI (Dundee; mean = 3.7°C). These winter temperatures rank the 9th warmest from the last 51 years at Edinburgh and the 21st warmest from the last 53 years at Dundee. Based on these figures, the predictions for the first flight of M. persicae is 1 June at Edinburgh (average date of first catch is 14 June) and 9 June at Dundee (average date of first catch is 13 June). Therefore, M. persicae activity in 2019 is expected to commence 1-2 weeks earier than in an average summer.
The warmer than average temperatures over 2018-19 winter indicate that the first flights of M. persicae should be about 1-2 weeks earlier than on average, and 2-3 weeks earlier than in 2018. Consequently, populations have the potential to develop to levels that could significantly threaten the virus health of seed crops. The prediction for the total of M. persicae caught by 31 July is 24 at Dundee and 33 at Edinburgh. The 75% confidence intervals for these predictions are 7 at the lower end for Dundee and 9 at the lower end for Edinburgh, and 81 at the upper for Dundee and 119 at Edinburgh. Therefore, populations of M. persicae could be relatively high during the growing season for potatoes in 2019. Therefore, given the increase in inoculum observed during 2018, there is a significant risk of further leaf roll transmission in potato crops in 2019, presenting a risk for the 2020 crop exhibiting significantly higher levels of leaf roll than the average of 5.5% predicted for 2018.
|First catch in 2019||30 April||28 May|
|1st catch prediction 2019||9 June||1 June|
|Mean date of first Catch||13 June||14 June|
|Catch to 9 June 2019||8||1|
|Predicted catch to 31 July 2018||24||33|
|Mean catch to 31 July||41||34|
Peach-Potato aphids in 2019
A total of six peach-potato aphids were caught in two of the Scottish suction traps between the 3 and 9 June, with five in Dundee and one in the new Inverness trap.
As of 9 June 2019, a total of 8 Peach-Potato aphids have been caught in the Dundee trap and 1 in the Edinburgh trap. The combined total ranks 6th when compared to the previous 32 years.
The first individual at Dundee was caught more than six weeks earlier than average, and 40 days earlier than predicted. This lies outwith (earlier than) the 75% confidence limits for both SASA and Rothamsted's prediction models.
The first individual at Edinburgh was caught on the 28 May, just over two weeks earlier than average and four days earlier than predicted (lying well within the confidence ranges).